I'm in the process of getting parts together for my upcoming rebuild but am in a quandry on what compression to run. I don't want or can afford to bore the cases so a big bore kit is out of my price range this time.
Here's my specs SO FAR:
Woods W6 cam, SE ignition, S&S E carb, Dyna coil, Hooker darkside slash cuts w/ baffles, I am NOT a stop light to stop light racer, but do like to twist the throttle from time to time! not much above 75 MPH on our ONE highway her in AK, daily commuter 15 miles to work in the summer, mostly single but some occasional 2 up riding. And a few weekend 600+ mile rides over the summer.
Any and all constructive comments & suggestions would be GREATLY appreciated.

 

I would like to hear the same answer from people who know. When we were doing my cam at my local indy, "he" proclaimed that 10:1 was the ideal compression for a street ridden Evo. Unfortunately he said that it was too much for the EV-27 cam we were installing at the time, and I needed to change cams if I ever decided to bump it up. But, that aside, he said 10:1 was best. That is all I know.

 

Either compression ratio you mention should be good with the set up listed. If going with 10:1 with the Wood 6 cam, you may want to consider a programmable ignition system for the ability to adjust the advance curves...(not sure about the fuel in AK.). Other than that, there is no performance gain by switching to a single fire system.
A quailty 2:1 exhaust system wouldn't hurt, either.

 

With the EV27, the intake closes at 36, which is a bit early for 10:1.
It would wind up pinging pretty badly.
You would want a timing event at 40 or later to bleed off some of the cylinder pressure to prevent detonation. I like a bit later than 40, but not too much or you run the risk of being a bit soft on the bottom end. The weight is of consideration at that point, IMO.

...and yes, 10:1 is an excellent compression ratio for the Evo motor....IMO, they should have come from the factory that way.

 

what '98 said...

and open up those heads a bit and you'll fair nicely with 10:1

 

I went with an EV46 for my FXRS, thinking light bike cam, I'll bump the CR to 10:1 and be golden. I haven't done anything with the heads but I did pop the cam in. Ran a quick compression check cold and I've picked up 10 psi cranking pressure. Didn't expect that but I'll take all the free CP I can get. I'll run it today and see how she feels and then it's off with the heads!

 

The compression question is in good hands already, Andrews are great cams and add another item to the already complicated cam decision world

My buddies 80" Evo light bike has raised compression, Andrews cam, mild headwork and can embarrass alot of bigger cubed bikes. I have a bigger motor, all of the mods and run even with him but I'm pulling a big bike and a 270 lb donut eating rider but the big picture is an 80" Evo with 10-1 and the basic supporting parts can hold it's own in the big fish pond.

On a note, when I had my heads done by John Sachs, he set my compression at 10-1 and mentioned that compresssion was optimal and still safe in the Florida heat where he lives, John has forgotten more than I will ever know and well respected in the Harley engine building world so his wisdom and my finished product in the real world riding is my guide to the compression the Evo section recommends.